Resonant circuit



Feb. 7, 1933, F. 1 ARLAND 1,896,993

RESONANT CIRCUIT Filed May l4} 1929 1,2 f 2 54 /6 lg ff ,f2 1 77 3/ 'N"INVENTOR wmgsis 5 jfl. ir/mw! 7/1 o BY jfl'egue/zcy ATTORNEYS PatentedFeb. 7, 1933 UNITED STATES PATENT OFFICE RESONANT CIRCUIT Applicationled May 14,

This invention relates to resonant circuits. It is among the objects ofthe present 1nvention to provide an improved resonant circuit adaptedfor use as a tuning circuit for i 5 the reception of Hertzian waves.

It is a further object of the present invention to provide a tuningcircuit, the resonance curve of which will have a flat top, thusproviding uniform amplification over a wide band.

It is a further object of the present invention to provide a radiofrequency tuning circuit arranged for uniform transmission of a wideband of frequencies.

It is a further object of the present invention to provide a radiofrequency tuning circuit which will uniformly amplify a band offrequencies of any desired width It is also an object of the presentinvention to provide a novel method of obtainin a resonance curve havingsubstantially at tops.

Other objects and features of the present g invention will be apparentfrom a consideration of the following specification taken in conjunctionwith the accompanying drawing, in which Figure 1 is a diagrammaticillustration of one arrangement of the present invention;

Fig. 2 is a view similar to Fig. 1, of a different arrangement of theinvention, and

Fig. 3 is an illustration of the resonance curve characteristic tocircuits formed in accordance with the present invention.

Referring more particularly to the drawing, the invention has beenillustrated in connection with a simple receiving circuit which has beenillustrated as including a single thermionic relay. It will beunderstood, however, that the present invention is applicable to cascadeamplification or in any type of radio or audio frequency work in which aresonant circuit is used.

Referring more specifically to Fig. 1 of the drawing, an antenna 10 hasbeen provided having a primary transformer coil 11. Associated with theprimary coil 11, a plurality of variously characterized secondarytransformer coils l2 are provided arranged in parallel with a variablecondenser 13. The

1929. Serial No. 362,992.

coils 12 and condenser 13 are arranged between the conductors 14 and 15to form a resonant circuit, the output of which is delivered to theusual thermionic relay 16, the conductor 14 being associated with a grid17, 55 while the conductor 15 is associated in the conventional mannerwith a filament 18. The vacuum tube is in the conventional mannerassociated with an output circuit which includes the conductors 19associated with 60 the grid and opposite side of the filament.

In considering the action of this form of the present invention, it willbe understood that the device is arranged for the reception of radiocarrier waves and the side bands which transmit the speech. In theconventional tuning circuits now in use, uniform amplification of thedifferent side bands is diticult due to the fact that the circuit whentuned to the carrier frequency, offers less resistance to the side bandsnea-rer the carrier wave than to those further remote therefrom. Thislack of uniform amplification of all the side bands naturally preventsperfect reproduction.

Vith the use of the present invention, a plurality of secondarytransformer coils having rwinding of slightly different impedance andtuned by the usual condenser 13, provide for simultaneous resonance atdifferent frequencies, the arrangement being such that the effect is aplurality of tuning circuits all feeding into the grid 17 of thethermionic relay and each circuit by virtue of the tuning by thecondenser 13 will be tuned in close 85 harmony but in such variance thatall the desired side bands will be faithfully amplilied in the relay.

Y Referring more particularly to Fig. 2 of the drawing, the form ofcircuit here illustrated includes the antenna 20, primary transformercoil 21 and a plurality of secondary transformer lcoils 22. In this formof the invention the secondary coils 22 are of uniform impedance andcharacteristics, each 9 of which is, however, associated with variouslycharacterized fixed condensers 22A, which in combination with thevariable condenser 23 and the conductors 24 and 25, provide a pluralityof variously characterized resonant circuits which may be simultaneouslytuned for close resonance, vvhereby the eifect as produced by that formof the invention shown in Fig. l Will result. rllhis circuit has beenshown as including a thermionic relay 26, grid 27, filament 28 andconductors 29, all substantially as shown and described in connectionwith F ig. l.

In connection With the present invention it Will be understood that theinvention'is applicable in resonant circuits other than inl acterizedparallel inductances or capacities Which Will have the effect ofproducing a plurality of individual resonances for the circuit.,V n.

Referring more particularly to Fig; 3, the type of resonance curve forthe circuit is here illustrated. llhus in a given place along thefrequency line the resonances at that point will permit the passage ofthe Wave of thatI frequency and thus the same may be amplified. ln usualcircuits, hoyvever, this curve converges rapidly toward a peak; thus asamplification increases faithful reproduction is lost as the side bandsare not amplitied because of their being cut od by the converging Wallsof'the resonance curve. Tvlfith the present circuit, however, it Will beseen that the resonance curve has a substantiallyV flat top and thusfaithful amplification will be had over the 'Whole height oftheresenance curve; The perfect ampliiication'curve is indicated in Fig. 3 bythe dotted lines 30, While the experimental curve found byapplicant is shown by the full lines 8l.

From the foregoing it Will be readily seen Ythat the invention hasprovided a novel and improved resonant circuit, together With a novelmethod of securing the straight topped resonance curve. lt Willbeunderstood that the invention is not confined to its applica-- ytionherein nor to the specific method of lsecuring the Wide amplificationband. Thus in the formation of the invention, numerous changes andmodifications and the-full use of equivalents may be resorted to Withoutdeparting from the spirit or scope of the invention as outlined in theappended claims.

`Vhat is claimed is: Il. A'radio receiving circuit, including a primarytransformer coil associated With the receiving aerial, andaplurality ofsecondary tive terminals connected across the respective Y i MJ-'ralcoils connected in parallel inductively related with said primary coilfor selectively receiving from said primary coil one band offrequencies.

2. A radioV receiving circuit, including a primary transformer coilassociated with the receiving aerial, a plurality of secondary coilsinductively related With said primary coil for selectively receivingfrom said primary coil one signal band of frequencies, said coilsbeingarranged in parallel in a detector circuit and tuning means connected tothe terminals of said secondary coils, said secondary coils and tuningmeans forming part of independent resonant circuits, eachindependentresonant circuit receiving apredetermined frequency band.

, 3. A radio receiving circuit, including a primary transformer coilassociated With the receiving aerial, a plurality ofsecondary coilsinductively related With said primary coil for selectively receivingfrom said primary coil one band of frequencies, vsaid secondary coilsVbeing arranged inparallel in a detector and circuit, and avariableicondenser arranged in said circuit parallel to all of saidsecondary coils.V

4. A radio receiving circuit, including a primary transformer coilassociated with the receiving aerial, a plurality of secondary coilsinductively related with said primary coil for selectively receivingfrom said primary coil one signal containing a band of frequencies,saidsecondary coils being arranged in parallel in a detector circuit,and

a tuning means arranged insaid circuit parallel to all Vof saidsecondary coils, said secondary coils selectively forming part ofindependent-resonant circuits including said tuning means,eachindependent resonant circuit receiving `a predetermined frequencyband. A y

5. A radio receiving circuit,`including a primary transformer coilassociated With the receiving aerial, a plurality ofsecondaryV coilsinductively related with :said primary coil for selectivelyreceivingfrom said primary Vcoil one signal containing a lband of frequencies,said secondary coils being arranged in parallel in a detector circuit,and

a variable condenser arranged in said circuit parallel to all ofv saidsecondary coils, said secondary coils selectively forming part ofindependent resonant circuits including said variable condenser, each ofsaid secondary coils having a .different impedance eachv of saidindependent resonant'circuits receiving a predetermined frequency band.

6. An electrical circuit including al primarycoil adapted to Vbeconnected Withan aerial, a plurality of secondary coils-in inductiverelation to saidprimary coil, each Asecondary coil having a dierentimpedance,

a single variable condenserhaving its respecterminals of all of saidsecondary coils, and an output circuit connected to the terminals ofsaid condenser said output circuit bein connected to the respectiveterminals of sai secondary coils and thereby forming with said condenserselectively independent resonant circuits, each independent circuitreceiving an independent frequency band.

7 A radio receiving circuit, including a primary transformer coilassociated with the receiving aerial, a plurality of secondary coilsinductively related with said primary coil for selectively receivingfrom said primary coil one band of frequencies, said secondary coilsbeing arranged in parallel in a. detector circuit, and tuning meansarranged in said circuit parallel to all of said secondary coils, saidsecondary coils selectively forming part of independent resonantcircuits including said tuning means, each of said independent resonantcircuits receiving a predetermined frequency band, said tuning meansbeing operable to vary each of said independent resonant circuits toreceive a si nal of a particular frequency Within the requency band ofeach of said independent resonant circuits.

8. A radio receiving circuit including a primary transformer coilassociated with the' receiving aerial, a plurality of secondary coilsinductively related With said primary coil for selectively receivingfrom said primary coil one band of fre uencies, said secondary coilsbeing arrange in parallel in an output circuit, and a variable condenserarranged in said output circuit parallel to all of said secondary coils,said secondary coils selectively forming a part of the independentresonant circuits, each of said independent resonant circuits receivinga predetermined frequency band.

FREDERICK L. ARLAND.

